Pneumopercussive cyclic action reversible self-propelled soil penetrating machines are known. In general, these machines comprise a hollow cylindrical body, having a pointed front part, a striker reciprocating inside the body, and an air distributing mechanism. A machine operation cycle includes a forward and backward stroke of the striker. In the forward mode of operation, the striker at the end of its forward stroke imparts an impact to the front end of the body resulting in an incremental body soil penetrating. During the backward stroke, the striker is braked by an air buffer in order to prevent or minimize an impact to the internal rear end of the body. In the reverse mode operation the striker is braked during its forward stroke to eliminate an impact. However, it accelerates during the backward stroke and imparts an impact to the internal rear end of the body so that the body moves backward a certain increment of displacement.
A pneumatic reversible machine of this type is described in U.S. Pat. No. 3,651,874 issued to Sudnishnikov et al. in March, 1972. The machine operation is based on a valveless air distributing mechanism causing relatively short strokes of the striker. The machine has inherent disadvantages which are discussed in numerous subsequent patents. The most significant disadvantages consist of insufficient impact energy resulting in high energy consumption at low productivity of the machine, non-reliable reverse mechanism, and low durability.
U.S. Pat. No. 3,708,023 issued to Nazarov et al. in January, 1973, and also U.S. Pat. No. 3,865,200 issued to Schmidt in February, 1975, relate to the impact energy problem. However, the solutions offered in these patents appear unsuccessful. Therefore, the impact energy problem associated with high energy consumption and low productivity remains unsolved.
U.S. Pat Nos. 3,727,701 (April 1973); 3,744,576 (July 1973); 3,756,328 (September 1973); 4,078,619 (March 1978); 4,214,638 (July 1980); issued to Sudnishnikov et al. illustrate the problems of the reverse mechanism suggesting some improvements. A series of U.S. Patents also dealing with the reverse mechanism has been issued to different authors during the past 15 years. However, the basic problems of the reverse mechanism associated with the control and extremely low impact energy of this mechanism remain unsolved. A detailed analysis of these patents is presented in the U.S. Pat. No. 5,031,706 issued to Spektor (the author of the present invention) in July, 1991. This patent also illustrates numerous additional disadvantages of the existing machines which are based on the U.S. Pat. No. 3,756,328.
Analysis of energy consumption and productivity of the working process of the existing machines (based on the research investigations, published by the present inventor), shows that the mentioned working process is characterized by relatively high energy consumption at relatively low productivity (average velocity). The theory of minimization of energy consumption of soil working cyclic processes, developed and published by the present inventor, indicates that the process of vibratory soil penetration can be optimized with respect to minimum energy consumption. (See: Minimization of Energy Consumption of Soil Deformation, Journal of Terramechanics, 1980, Volume 17, No. 2, pages 63 to 77; Principles of Soil-Tool Interaction, Journal of Terramechanics, 1981, Volume 18, No. 1, pages 51 to 65; Motion of Soil-Working Tool Under Impact Loading, Journal of Terramechanics, 1981, Volume 18, No. 3, pages 133 to 136; Working Processes of Cyclic-Action Machinery for Soil Deformation-Part I, Journal of Terramechanics, 1983, Volume 20, No. 1, pages 13 to 41; Minimum Energy Consumption of Soil Working Cyclic Processes, Journal of Terramechanics, 1987, Volume 24, No. 1, pages 95 to 107). Applying the mentioned theory to the existing machines in order to optimize the parameters shows that the impact energy of the striker should be significantly increased. This could be achieved by an appropriate increase of the stroke of the striker (without increasing the nominal pressure of the compressor). However, the valveless air-distributing mechanism of the existing hole making machines makes it almost impossible to increase the stroke of the striker to a considerable extent. A detailed discussion of this problem is presented in U.S. Pat. No. 5,031,706 offering a reversible soil penetrating machine provided by an air-distributing mechanism that should allow for a relatively long stroke of the striker. The housing of the mentioned machine has three longitudinal slots machined on its external lateral surface. These slots are hermetically covered and are used as air passages. According to an alternative embodiment, the housing consists of an outer and inner tube. The inner tube, having tree longitudinal slots on its external surface, is pressed into the outer tube creating three separate longitudinal channels. One of these channels alternatively delivers compressed air to the backward stroke chamber during the backward stroke of the striker or connects the backward stroke chamber with the atmosphere during the forward stroke of the striker. The second channel is used for exhaust of the compressed air from the forward stroke chamber at the end of the forward stroke of the striker in the forward mode operation of the machine. The third channel is intended for exhaust of compressed air from the forward stroke chamber at the forward stroke of the striker in the reverse mode of operation.
The front anvil of this machine comprises a moveable chisel. The striker is reciprocating inside of inner tube. The rear anvil represents a part of the air-distributing mechanism. This mechanism has a spring loaded stroke control valve that cyclicly reciprocates opening and overlapping appropriate ports, directing the compressed air to the forward or backward stroke chambers, and also connecting the backward stroke chamber with the atmosphere. The air-distributing mechanism comprises three separate air hoses. One hose delivers compressed air at the nominal pressure which is used for the forward stroke of the striker and also for governing the stroke control valve. The second hose delivers compressed air at a reduced pressure which is only used for the backward stroke of the striker (the lowered air pressure does not take part in governing the stroke control valve). The third hose delivers compressed air at the nominal pressure to a spring loaded mode control valve and switches over the machine from forward to reverse mode operation.
Several prototypes of this machine have been built and tested. These prototypes demonstrated very low efficiency at the forward mode operation due to insufficient impact energy of the striker. The testing procedures made it possible to understand and to explain the reasons why the striker was not gaining the precalculated energy during its forward stroke. The explanations are as follows. It was assumed that during the forward stroke of the striker the pressure in the forward stroke chamber should have been equal or close to the nominal pressure. At this condition, the air pressure on the left and right ends of the stroke control valve would have been equal and the valve would have been held in its extreme left position being pushed by the spring. This would have allowed the striker to be accelerated all the way along the length of the forward stroke chamber. However in reality, this assumption is incorrect. The tests show that during the forward stroke of the striker the pressure in the forward stroke chamber starts to drop shortly after the striker begins to move forward. The left end of the striker is at all times under the nominal pressure of the system. As soon as the pressure inside the forward stroke chamber, which is connected with the right end of the valve, drops to a level where the nominal pressure force applied to the left side of the valve exceeds the spring compression force, the valve moves to its extreme right position. This stops the air supply to the forward stroke chamber and opens the ports for compressed air delivery to the backward stroke chamber. The striker, still being far away from the end of its forward stroke, is now braked by the compressed air in the backward stroke chamber. All this causes a low impact energy of the striker. It is obvious that the striker would have more impact energy if its stroke would be longer. However, the prototype built according to U.S. Pat. No. 5,031,706 actually also has a short stroke mechanism which, as it is shown above, does not provide sufficient impact energy required for optimization of the working process of the underground hole making machines.
The attempt to apply a stronger spring to the stroke control valve was also unsuccessful. The stronger spring caused an early switch over from the backward stroke to the forward stroke of the striker, which resulted in a shortening of the forward stroke, and consequently, reduced the efficiency of the working process.
Thus, the energy problem associated with the minimization of the energy consumption at an increase of the productivity of the working process of the underground hole making machines remains unsolved.
Another disadvantage of the considered machine is associated with the control of forward and reverse mode operation. The need of the third air hose, the mode control valve, and the separate exhaust channel for the reverse mode operation complicates the machine, increasing the cost of its manufacturing and maintenance. In addition to this, it should be noted that the tests have shown that the available cross-sectional area of the exhaust channel for the forward mode operation is insufficient. An essential air pressure remains inside the forward stroke chamber after the exhaust. This causes an early switch over from the backward stroke to the forward stroke, decreasing the stroke of the striker.
A further disadvantage of the considered machine is the need of special equipment for pressing in the inner tube into the outer tube. These tubes are relatively long and require unconventional and costly equipment to press one tube into another.
Another disadvantage of the considered machine is associated with the annular resilient gasket which is intended to prevent penetration of soil between moveable components of the chisel assembly. This gasket is located on a cylindrical surface and is compressed in the axial direction by two components which are in relative cyclic reciprocation during the machine operation. Thus this gasket is subjected to cyclic loading and is often pushed out from its original location, and sometimes it cracks and moves away.
Another disadvantage of the considered machine is associated with the need of a complicated solenoid type frequency sensor.
Still another inherent disadvantage of known reversible underground hole making machines is that in the reverse mode operation the striker imparts impacts to the rear anvil which represents a part of the air-distributing mechanism. These impacts are transferred to the tail nut of the machine through the body parts of the air-distributing mechanism. This often causes loosening of the nut with a subsequent failure of the air-distributing mechanism. Besides this, the mentioned body parts should be made of strong materials with high toughness.
One more inherent disadvantage of conventional underground penetrating machines is the lack of means to signal about the deviation from the initial trajectory.
The present invention offers solutions to eliminate these disadvantages. These solutions are based on the testing of full scale real prototypes in laboratory and field conditions. The results of testing convincingly confirm the reliability and efficiency of the incorporated engineering solutions.
Implementation of the present invention will significantly increase the efficiency of the working process of the underground pneumatically operated self-propelled soil penetrating machines.